Forest Floor Thickness Research Articles

Влияние реконструктивной рубки в лиственно-еловом древостое на корневую конкуренцию пород

The predominance of mixed forest stands in a productive forest fund, which is located in the middle taiga subzone of Northwest Russia, determines the relevance of an investigation of the growth and development characteristics of the trees. In secondary stands, created by an extensive human consumption of primary spruce stands, spruce trees are generally presented in a minor quantity. The recovery of their dominance is an urgent economic and ecological issue. Despite the unity of approaches concerning the maintenance of deciduous-spruce forests, the research characteristics on the structure of the root systems differ considerably along with age and geographical position. This article investigates a root system competition between spruce and deciduous species in a 70-year-old blueberry-type forest that was 100 thinning by a reconstructive cutting 35 years ago. The mass of fine roots and their distribution in the upper solid layers were examined by the method of soil monoliths in the mixed stands with different proportions of spruce. The numerical characteristics of the stands were determined by the results of a regular complete enumeration on the trail plots. Besides, the tree diameters were measured around the circular plots, which were made for the collection of the monoliths. The records were made on the dynamics of changes in forest floor thickness and vegetation. The relationship between the underground and elevated parts of the stands was explored. It was shown that the roots of spruce can occupy the same ecological niche as the roots of deciduous species. A correlation analysis revealed a statistically significant relationship between the mass of fine spruce roots and the competitive influence of deciduous species, the proportion of spruce in the stand, and its current volume increment. There was a significant difference in spruce root mass under joint growth with birch and aspen. Therefore, it was concluded that this phenomenon has a complex nature. Namely, the mass of the spruce roots has a direct dependency on their closeness to the maternal trees in combination with the spatial heterogeneity of the organic soil layers. The gained findings are important for the regulation of the composition and structure of the mixed deciduous-spruce stands for growing sustainable stands with a high economic value. For citation: Karpechko A.Yu., Sinkevich S.M. Influence of Reconstructive Cutting in Deciduous-Spruce Stands on Root Competition of Species. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 3, pp. 99–112. (In Russ.). https://doi.org/10.37482/0536-1036-2023-3-99-112

THE IMPACT OF REFORESTATION ON PHYSICAL AND HYDROPHYSICAL PROPERTIES OF SOILS OF THE FALLOW LANDS (SKOLIVSKI BESKYDY, THE UKRAINIAN CARPATHIANS)

The article tackles the impacts of anthropogenic load on the physical and hydrophysical soil properties. In order to better comprehend the processes of spontaneous sylvatisation in a mountain region (the Pohartsi boundary, Koziova village, the Skolivski Beskydy physiographic region) four study plots were selected representing the successional sequence: forest → pasture → hay meadow → arable lands. Land patches that were affected the least by anthropogenic load restored faster to their natural baseline conditions. Tilling appeared to retardate restoration processes, however those anyway took place. Proper functioning of arable land patches may be facilitated by continuous land care actions (i.e. ploughing or mowing).We found that soil bulking density in arable lands increased in upper soil horizons compared to forest ecosystems. Such an increase is caused by mechanical turning upper soil horizons up down and vice versa, for lower horizons. In pasture lands, upper soil horizons are trampled down by livestock. This leads to lower water permeability of soils: increase in soil bulk density from 0.79 to 1.15 g•cm-3 resulted in a decrease of water permeability by 75 %. In forested lands, values of water permeability similar to those in arable lands (0.55 mm•min⁻¹) are usually observed along the walking trails and in wood trilling plots. On the land patches with scarce herbaceous cover erosion processes are emerging. The latter is especially dangerous for arable land patches causing extra leak of soil nutrients and thus soil depletion. In order to further exploitation soils in such patches need additional fertilizing. As agricultural load diminishes soil upper horizons restore. Restoration occurs through prolonged freezing and thawing cycles during the cold (autumn-winter-spring) season. Another path for soil physical properties restoration is associated with penetration of plant fine roots that loosen the soil. Increase of total sparing indices is observed, as well. For upper horizons of restored soil it is assessed as “intermediate” (62,00 ‒ 65,35 %) whilst for arable land patches it is significantly lower (54,90 %). Soil bulk density gradually decreased along soil profiles and study plots. In forested patches it reached minimum (2,28 g•cm⁻³) and in arable land patches – maximum (2.55 g•cm⁻³) values, which did not change upon termination of anthropogenic load. Significant changes were observed for the field humidity indices. These varied both spatially, along soil profiles, and temporarily, by seasons. Lack of herbaceous vegetation caused over-drying in upper soil horizons. At the same time in lower horizons field humidity increased. Upper soil horizons in forested patches undergo the least changes due to the presence of thick forest floor. We conclude that major indicators of agricultural load within a soil profile are soil bulk density, water permeability and total sparing. Such indicators as the solid phase density and field humidity are of additional value. Key words: reforestation; soil bulk density; water permeability; soil profile; arable lands; pastures; Skolivski Beskydy.

Thick forest floors in the Calcareous Alps – Distribution, ecological functions and carbon storage potential

The thickness and composition of forest floors plays an essential role for the efficiency and resilience of mountain forests to store carbon, water and nutrients. Up to now, the distribution of particularly thick organic forest floors (TOFF) in the Bavarian Calcareous Alps is poorly known and their ecosystem services deserve increased consideration under climate change. We wanted to improve the knowledge of the TOFF-distribution and to investigate the forcing processes and ecological functions of TOFF. We aimed to quantify their carbon storage potential and to model areas in which humus management is mandatory for sustainable forest use. We drew a stratified sample of soil profiles. Through the combination of relief and soil parameters, we identified crucial control variables and modelled actual and potential (without human disturbance) forest floor thickness in the Bavarian Calcareous Alps based on quantile regression and Generalized Additive Models (GAM). TOFF were predicted to occur on approximately 10% of the forest area of the Bavarian Alps. A decisive condition for the development of TOFF was the absence or only shallow development of mineral fine soil. Contrary to conventional wisdom, these TOFF were found across a wide range of (montane to subalpine) elevations. C-storage of TOFF amounts to ca. 6.9 t C/ha per cm of humus depth and ca. 5.2 Mt C in the study area, resulting in C accumulations comparable to peatlands. TOFF are decisive for the delivery of ecosystem services, especially in the protection forests of the Bavarian Calcareous Alps. Due to the absence or ephemeral depth of mineral soil, all ecological functions depend solely on the forest floor. Therefore, the careful handling of the humus stock is mandatory for a sustainable management in these forests.

AN ECOLOGICAL ASSESSMENT OF THE STATE OF SMALL RIVERS IN THE MIDDLE TAIGA SUBZONE OF KARELIA

A multidisciplinary survey of three small rivers emptying to Lake Onego was carried out; information was collected regarding the aquatic biota, the species and age structure of riparian forests, their floristic diversity, and soils. The integral indicator chosen to assess the ecological condition of the watercourses was the characteristics of the rivers’ fish fauna, in particular fish of the Salmonidae family. Surveys of the rivers and riparian forest communities yielded records of 181 vascular plant species (11 of them macrophytes), 11 moss species, 2 lichen species; the fish fauna was made up of 9 species. Overall, the riparian forests featured a relatively wide range of typological diversity. The tree stands varied from the poor Ledum types (site class V) to the most productive Oxalis types (site classes III–I). Analysis of the tree species and age structure of forests in the riparian buffers revealed a prevalence of stable coniferous tree stands in good condition. Statistically reliable correlations were detected between the fish fauna and the tree species composition and inventory characteristics of the riparian forest stands, soil morphological characteristics, and the species diversity of the living ground cover and macrophytes. The species diversity of the riparian and the aquatic biotas were found to correlate positively with each other. Fish numbers were seen to negatively correlate with some characteristics of riparian forest soils (forest floor thickness, podzolic horizon), while the correlation with the humus horizon thickness was positive. Significant positive correlations were identified between aquatic organisms (fish, zoobenthos) and a majority of the stream’s hydrological parameters. The resultant up-to-date information about water-forest system components is important for understanding the role of small streams, which, alongside the scant officially recognized “spawning” rivers, are an ecological niche in the life cycle of salmonid fishes in Northwest Russia.

Рекреационные изменения компонентов лесных экосистем на примере объекта культурного наследия «Беломорские петроглифы» (Республика Карелия)

Recreation digression of forest ecosystems in the heritage site “White Sea Petroglyphs” was studied for the first time. This site is a compact system of rock outcrops partially cleared of forest vegetation, which bear Neolithic rock carvings (petroglyphs), and are linked together by walking trails. Patterns have been identified in the transformation of soils, plant cover components (tree stand, tree seedlings, understory and living ground cover), as well as fine roots (within 3 mm in diameter) of woody species under the recreation impact. Trampling was found to deform and destroy the top soil horizons, entailing a significant loss of the forest floor thickness and organic matter stores. Overall, the flora of the area is quite well preserved; 95–100 % of which is represented by native species. The living ground cover is noticeably damaged in the most actively used sites (fragments of trails and vista points). They feature a poor species composition, shrinking of the herb-dwarf shrub and moss-lichen cover, and a low percent cover of grassland and ruderal species. Easily accessible and actively visited sites have no or reducing amounts of tree seedlings, the tree stand is damaged and forest regeneration is hampered – the number of viable seedlings is minimal (100 pcs/ha). The mass of roots below 3 mm in diameter in heavily trampled trails showed a reduction of up to 74 %, while the root saturation in less affected trails slightly increased. Recreation transformations of the plant communities have not resulted in a loss of their resilience so far. The recreational digression in the studied sites was classified into stages I–III (weakly disturbed – strongly disturbed). Function zoning of the area should be modified using recreation-tolerant communities more intensively in order to reduce recreation impact. The most damaged areas, which are losing their stability, should be excluded from active use by modification of walking trails and building additional boardwalks.

Spatial variability of forest floor and topsoil thicknesses and their relation to topography and forest stand characteristics in managed forests of Norway spruce and European beech

Soils play a significant role in climate regulation, especially due to soil organic carbon (SOC). The SOC pool is therefore modeled for various environments, and forest floor and topsoil thicknesses are important parameters for most of these models as they store most of the SOC. However, the forest floor and topsoil thicknesses show high spatial variability which is a result of multiple factors which are not agreed upon among scientists. Out of these factors, we choose topography parameters (elevation, slope, and topography wetness index) and forest stand characteristics (stand age, dominant tree species, and forest floor cover), and soil moisture, and we analyzed their relationship to the forest floor and topsoil thicknesses. The study was performed in a managed submontaneous forest in Central Europe dominated by Picea abies (L.) Karsten with small patches of Fagus sylvatica L. or other species. The thicknesses of the O horizons (Oi, Oe, Oa) and topsoil were measured at 221 sampling pits. Geographically weighted regression showed that the spatial variability of the overall forest floor plus topsoil thickness (OA) is responsible for 8% of its variability. The thickness of the OA is the most strongly controlled by forest floor cover explaining approximately 6% of its variability and soil moisture explaining 2–6% of the variability. The Oi + Oe horizon thickness is controlled only by forest floor cover explaining 10.7% of its variability, and the thickness of Oa + A horizon can be explained mainly by soil moisture in mineral horizon explaining 9% of the variability.

Plant indicators for Folic Histosols in mountain forests of the Calcareous Alps

AbstractQuestionsAlthough thick forest floors overlying unweathered bedrock are important resources for mountain forests' functioning, their actual distribution is poorly known and difficult to delimit in the field. We therefore asked: (a) What is the specific composition of vegetation growing on Folic Histosols; (b) can indicator plants be used to detect Folic Histosols in mountain forests; (c) what do functional traits of plant indicators tell about the ecological properties of Folic Histosols?LocationNorthern Calcareous Alps, south Germany.MethodsBased on representative stratified sampling of joint vegetation plots and soil profile descriptions, we estimated the frequency and thickness of Folic Histosols, determined the proportion of compositional variation specifically attributable to forest floor thickness using ordination, applied Indicator Species Analysis and searched for typical traits and ecological requirements of indicator species.ResultsThe co‐existence of acidophilic and calciphytic plants is typical for the tessellated occurrence and the successional origin of Folic Histosols. In the study region, the detection of Folic Histosols on pure limestone or dolomite by ground vegetation works very well. Particularly acidophilic plants are suitable indicators for thick forest floors. The indicator value of bryophytes and Ericaceae for Folic Histosols is likely related to the colonization of rotten wood. Folic Histosol indicator species are widely spread in the allocation to sociology group, which ranges from open landscapes to dark forests and reflects successional origin.ConclusionsIn mountain forests on carbonate bedrock, thick humus layers often occur next to bare rock. This tessellated structure can also be detected in the ground vegetation, where acidophilic and calciphytic plants occur side by side. Thick Folic Histosols in late successional forests are dominated by acidophilic plants colonizing rotten wood. Thus, the detection of Folic Histosols by understorey species is an easy and cost‐effective possibility and one key to protect these vulnerable forest sites.

MICROBIOLOGICAL CHARACTERISTICS OF SOILS UNDER VEGETATION MICROGROUPS IN A MIDDLE-TAIGA COWBERRY PINE FOREST IN KARELIA

The study was carried out in the Kivach Strict Nature Reserve situated in the middle taiga of Karelia. Albic Podzols formed over fluvioglacial sandy deposits in different vegetation microgroups (lichen-, cowberry-, bilberry-, true moss-dominated) within a cowberry-type pine stand were surveyed. The organic and mineral horizons of these soils were examined for the structural and functional setup of the microbial community. The key groups of microorganisms effecting nitrogen and carbon cycling and fluctuations in bacterial numbers were determined in soils formed under the different vegetation microgroups. The composition of the cellulolytic component of the microbial community was identified, and its variation among microgroups was demonstrated. It was found that the main contributor to soil respiration of the biogeocoenosis is microorganisms in the top organic horizon, while the activity of microorganisms in the mineral part of the soil is inhibited. Variations in some ecophysiological parameters of the soil microbiota, such as basal respiration, microbial biomass carbon (Cmic) and nitrogen (Nmic) and others, depend on soil moisture content and forest floor thickness. The data obtained through these integrated studies of the soil microbial community can be used in environmental monitoring.

Labile soil organic matter changes related to forest floor quality of tree species mixtures in Oriental beech forests

Abstract Labile soil organic matter, which is an important supply of energy for soil micro-organisms, has been suggested as a sensitive indicator of soil organic matter (SOM). In this study, the effects of forest vegetation on forest floor thickness and quality, labile SOM fractions and soil properties were examined in five different forest ecosystems, such as beech-hornbeam-alder, beech-hornbeam, beech-alder, beech-oak, and pure beech in the Hyrcanian region, northern Iran. Each forest type was replicated three times. In each plot, six forest floors and soil samples were taken in a 30 × 30 cm area. Pure beech had always a higher forest floor thickness than the other studied forest types. Increase in tree diversity in beech forest type reduced forest floor C:N ratio, more than three-fold, compared to pure beech. Based on our data, the influence of forest type on labile SOM was generally higher in the 0–10 cm soil layer than in the 10–20 cm layer. Beech-hornbeam-alder and beech-alder forest types, with high quality of forest floor and more values of N fractions in labile SOM, increased soil biological activities and fertility whereas pure beech and beech-oak forest types, with lower quality of forest floor and more values of C fractions in labile SOM reduced soil biological activities and fertility. Based on the result, the abundance of beech influenced nutrient cycling via forest floor quality. This led to an increase in labile SOM and subsequent soil fertility through the admixture of broadleaf species into beech forests.

Oribatid mite recovery along a chronosequence of afforested boreal sites following oil sands mining

Bitumen extraction via surface mining has affected nearly 1000 km2 of boreal forest habitat in the Athabasca oil sands region of Alberta, Canada, pushing entire ecosystems back to the primary stages of forest and soil succession. Previous work in the Athabasca oil sands region has investigated the influence of vegetation, mineral reclamation material, and peat cover soil on microbial communities and the quality of soil carbon. No research has been conducted to assess the bioindicator potential of soil fauna, specifically oribatid mites, in these reclaimed soils. This study investigated the influence of time-since-reclamation (8–31 yrs.) and canopy type (white spruce (Picea glauca (Moench) Voss), trembling aspen (Populus tremuloides, Michx)) on the abundance and diversity of oribatid mite adults ≥300 μm in size after land reclamation in the Athabasca Oil Sands Region. Thickness of the forest floor accumulating on top of the peat cover soil at the reclaimed sites was the most powerful predictor of oribatid mite richness, and was a better predictor than time-since-reclamation. A forest floor with a thickness ≥2 cm strongly increased oribatid mite abundance to levels higher than those found in the forest floors of natural, undisturbed stands in the area. Species richness in the (≥2 cm thick) forest floor within reclaimed stands was slightly lower than within natural stands but was notably higher than in the peat cover soil. Assemblage diversity followed the same trend as species richness, and mite diversity in the forest floor with a thickness ≥2 cm in reclaimed stands was the most similar to natural stands. Four of the six reclaimed stands with a forest floor thickness ≥2 cm were aspen stands, and increased aspen density may aid in faster reestablishment of oribatid mite communities after oil sands mining.

Forest Site Classification in the Southern Andean Region of Ecuador: A Case Study of Pine Plantations to Collect a Base of Soil Attributes

Forest site classification adapted to the respective site conditions is one prerequisite for sustainable silviculture. This work aims to initiate the forest site classification for pine plantations in the southern Andean region of Ecuador. Forest productivity, estimated by the dominant height of 20-year-old trees (DH20), was related to data from climate, topography, and soil using 23 plots installed in pine plantations in the province of Loja. Forest site productivity was classified as: low (class C: 13.4 m), middle (class B: 16.6 m), and high (Class A: 22.3 m). Strong determinants to differentiate the forest site classes were: the short to medium term available Ca and K stocks (organic layer + mineral soil standardized to a depth of 60 cm), soil acidity, the C:N ratio, clay and sand content, forest floor thickness, altitude, and slope. The lowest forest productivity (Class C) is mainly associated with the lowest short to medium term available K and Ca stocks. Whereas, in site classes with the highest forest productivity, pines could benefit from a more active microbial community releasing N and P, since the soil pH was about 1 unit less acidic. This is supported by the lowest forest floor thickness and the narrowest C:N ratio.

A Newly Identified Role of the Deciduous Forest Floor in the Timing of Green‐Up

AbstractPlant phenology studies rarely consider controlling factors other than air temperature. We evaluate here the potential significance of physical and chemical properties of soil (edaphic factors) as additional important controls on phenology. More specifically, we investigate causal connections between satellite‐observed green‐up dates of small forest watersheds and soil properties in the Adirondack Mountains of New York, USA. Contrary to the findings of previous studies, where edaphic controls of spring phenology were found to be marginal, our analyses show that at least three factors manifest themselves as significant controls of seasonal patterns of variation in vegetated land surfaces observed from remote sensing: (1) thickness of the forest floor, (2) concentration of exchangeable soil potassium, and (3) soil acidity. For example, a thick forest floor appears to delay the onset of green‐up. Watersheds with elevated concentrations of potassium are associated with early surface greening. We also found that trees growing in strongly acidified watersheds demonstrate delayed green‐up dates. Overall, our work demonstrates that, at the scale of small forest watersheds, edaphic factors can explain a significant percentage of the observed spatial variation in land surface phenology that is comparable to the percentage that can be explained by climatic and landscape factors. We conclude that physical and chemical properties of forest soil play important roles in forest ecosystems as modulators of climatic drivers controlling the rate of spring soil warming and the transition of trees out of winter dormancy.

Nitrogen and ash elements content in sub-horizons of forest floor

Nitrogen (N) and ash elements contents of forest floor (FF) depend on the fractional and chemical composition of falling litter. The elemental content in FF may be influenced as well by originated from the epipedon mineral particles due to soil fauna mixing activity. In actual work the contents (concentration and stocks) of N and ash elements were analysed in relation to phytogenic FF. In relation to total FF, the FF thickness, acidity, base saturation stage and C:N ratio as general characteristics were studied. The concentrations and amounts of N and ash elements of FF were studied on Gleyic Albic Fragic Glossic Retisols (group I), on Gleyic Albic Podzols (II) and on Ortsteinic Histic Podzols (III). The FF chemical parameters were researched in forest ecosystems with premature and mature (i.e. stabilized) forest stands. The dividing of FF into sub-horizons was possible only on soils with low soil faunal activity. The FF and its sub-horizons (OL, OF, OH) were sampled with a metallic frame (25×40cm). In the field conditions, the FF thickness (cm) and mass superficial density (gm−2) at field moisture content were determined. In the laboratory, the total and phytogenic FF dry mass superficial densities (Mgha−1) and their elemental contents (concentration – gkg−1 and amounts – kgha−1) were calculated. Content of N in FF samples was determined by Kjeldahl; content of K with flame-photometer; P by colorimetric method; Ca and Mg by complexometric titration with trilon B (using flame-photometer); Fe and Al colorimetrically, whereas in the case of Fe the sulfosalicylic acid and for Al the aluminon was used; the Si and remains were determined with weighing method. The soils of groups’ I and II are well drained aeromorphic, but group III hydromorphic. By WRB the soils of group I are Retisols, but soils of two rest groups - Podzols. The soils of group I have been formed on loamy sand under-layered by loam, but the texture of groups II and III soils is sand. By the humus covers the soils of group I may be classified as fresh and moist moder, of group II as fresh and moist mor and of III as wet and peaty mor. On soils of groups II and III only the pine forest, but on soils of group I as well the spruce forest are presented. In all three soil groups the sequence of chemical elemental concentration in OL horizon (as falling litter) was: N>Ca>Si>Mg>K= Fe=P>Al. In the course of further FF developments, the concentrations Si, Al and N are increased in considerable extent. Practically to the same level persist the concentrations of K, P and Mg. At the end of throughout flow of FF this sequence was: Si>N>Ca>Al>Fe>Mg>K=P. The greatest amounts of all studied elements were observed in the FF of soils’ group III on which the humus cover of wet and peaty mor type has been formed. The formation of this type of humus cover indicates the stagnation of elemental cycling between plant cover and soil cover.

The relationships of soil total nitrogen concentrations, pools and C:N ratios with climate, vegetation types and nitrate deposition in temperate and boreal forests of eastern Canada

Forest soils contain large organic N pools which might react to global warming and eventually impact C sequestration in these ecosystems. Quantifying these N pools and understanding the factors controlling their size is therefore crucial. Here, we report on C:N ratio, N concentrations and pools in the forest floor (FF) and the mineral soil (MS) horizons of 21 forests of eastern Canada and on their relationships with 13 biophysical variables. The C:N ratio decline with soil depth at most sites. Total soil C:N ratio ranged from 9.8 to 24.9 and increased with mean annual precipitation (MAP) and decreased with the percentage of hardwoods (Phwd). Total soil N pools to the C-horizon ranged from 475 to 1261gNm−2, and on average, 82% of soil N was located in the MS. Nitrogen storage in the FF increased with MAP, the percentage of conifers (Pc) and altitude, whereas it decreased with mean annual air temperature (MAAT) and FF pH. These relationships mainly resulted from the impact of these variables on FF thickness. Nitrogen pool in the MS was strongly positively correlated with N-NO3 deposition. Together with mean annual soil temperature (MAST), N-NO3 deposition was also positively correlated with total soil N storage. The depth at which half of the mineral soil N pool was reached (D50) averaged 20cm and increased with altitude, Pc and MAP:PET while it decreased with MAAT. These results show that while MAP and N-NO3 deposition are major drivers of N pools in the FF and the MS respectively, the distribution of N within the MS was rather explained by MAAT and the vegetation type. These data also suggest that increasing temperature might increase N sequestration in eastern Canadian forest soils in the future.

Short-term response of Cladonia lichen communities to logging and fire in boreal forests

Fire is the major disturbance agent in boreal forests that initiates forest regeneration and succession, and plays a major role in determining the composition of terricolous lichen communities. In recent decades however, logging has become an important disturbance agent in boreal forests. In this context, growing concerns about logging effects on endangered species such as woodland caribou (Rangifer tarandus caribou) has emerged and drawn attention on how reindeer lichens (i.e. Cladonia arbuscula, Cladonia mitis, Cladonia rangiferina, Cladonia stellaris, and Cladonia stygia) respond to logging and fire given their importance as winter forage for caribou. We compared critical lichen habitat factors (i.e., forest floor thickness, tree height, and canopy closure) between fire and logged sites and evaluated how Cladonia lichen species richness, biomass, and ground cover were related to these habitat factors in the first decades following disturbance. We found no significant differences in habitat factors and no significant differences in lichen species richness or ground cover between logged and fire sites. However, Cladonia lichen biomass was significantly higher following logging. These results support the hypothesis that Cladonia lichens can persist following logging and suggest that forestry practices that include in their toolbox winter harvesting or machinery traffic restricted to specific trails are likely to preserve undisturbed forest floor habitat conditions with source populations of lichens.

Understory Plant Community Composition Is Associated with Fine-Scale Above- and Below-Ground Resource Heterogeneity in Mature Lodgepole Pine (Pinus contorta) Forests.

Understory plant communities play critical ecological roles in forest ecosystems. Both above- and below-ground ecosystem properties and processes influence these communities but relatively little is known about such effects at fine (i.e., one to several meters within-stand) scales, particularly for forests in which the canopy is dominated by a single species. An improved understanding of these effects is critical for understanding how understory biodiversity is regulated in such forests and for anticipating impacts of changing disturbance regimes. Our primary objective was to examine the patterns of fine-scale variation in understory plant communities and their relationships to above- and below-ground resource and environmental heterogeneity within mature lodgepole pine forests. We assessed composition and diversity of understory vegetation in relation to heterogeneity of both the above-ground (canopy tree density, canopy and tall shrub basal area and cover, downed wood biomass, litter cover) and below-ground (soil nutrient availability, decomposition, forest floor thickness, pH, and phospholipid fatty acids (PLFAs) and multiple carbon-source substrate-induced respiration (MSIR) of the forest floor microbial community) environment. There was notable variation in fine-scale plant community composition; cluster and indicator species analyses of the 24 most commonly occurring understory species distinguished four assemblages, one for which a pioneer forb species had the highest cover levels, and three others that were characterized by different bryophyte species having the highest cover. Constrained ordination (distance-based redundancy analysis) showed that two above-ground (mean tree diameter, litter cover) and eight below-ground (forest floor pH, plant available boron, microbial community composition and function as indicated by MSIR and PLFAs) properties were associated with variation in understory plant community composition. These results provide novel insights into the important ecological associations between understory plant community composition and heterogeneity in ecosystem properties and processes within forests dominated by a single canopy species.

Linkage between exotic earthworms, understory vegetation and soil properties in sugar maple forests

The comminuting and soil mixing activities of earthworms can affect soil physical, chemical and biological properties, which in turn can influence plant growth and survival. Accordingly, there is growing concern that the spread of exotic earthworms into northern temperate forests may compromise biodiversity and tree species recruitment. We report on a study where we sampled earthworms, soils, and understory plants in plots established in 40 mature sugar maple stands distributed over 3 areas in the Eastern Townships of Southern Québec (Canada). Earthworms were found in 19 of 40 plots, and earthworm frequency of occurrence (Efo) as well as the complexity of earthworm communities reflected human accessibility to the plots. Plant species richness decreased, and species evenness increased, with Efo. The Efo was related to a decrease in the cover of 5 plant species, and to an increase in the cover of 2 other plant species or plant functional groups. Increasing Efo also correlated with higher soil pH, lower forest floor thickness and lower soil C:N ratio. Among these 3 variables, redundancy analysis (RDA) revealed that soil pH and forest floor thickness correlated with plant community composition. Based on neutral lipid and phospholipid fatty acid profiles, we found that soil bacteria and fungi increased with a decrease in forest floor thickness, bacteria and arbuscular mycorrhizal fungi (AMF) increased with soil pH, whereas actinobacteria and AMF increased with Efo. We discuss the possible mechanisms by which earthworms might directly or indirectly alter understory plant community composition. By considering the location and land use management of each study site, our study provides further evidence that the spread of exotic earthworms in sugar maple stands of Southern Québec may be linked to human activities, with implications for further research and conservation issues.

Ghosts of the forest: Mapping pedomemory to guide forest restoration

Soil morphology can provide insight into how ecosystems change following periods of extensive disturbance. Soils properties can often be linked to historic environmental influences (e.g., vegetation or climate) to provide a record of pedomemory. Identification and mapping of soil pedomemory properties show promise in providing context for ecological restoration. We have developed a novel use of digital soil mapping of spodic morphology to estimate historical forest composition in the high-elevation forests of the Central Appalachians. This region was extensively disturbed by clear-cut harvests and related fires during the 1880s–1930s. Hardwood forest species recovered much better than local conifers and generally encroached into historic populations of red spruce (Picea rubens) and eastern hemlock (Tsuga canadensis). Spodic soil morphology, which is often associated with subalpine and boreal conifer forests, was mapped using a random forest probability model and showed correspondence to red spruce — eastern hemlock distribution, as derived from local historic property deed witness tree records from 1752 to 1899. These data and resulting models indicate a greater spatial extent of spodic soil properties than documented in previous soil maps, which is more consistent with general theories of much more extensive historic spruce populations. The resulting maps and models provide guidance for field scale restoration planning for historically disturbed spruce–hemlock forests. Our results suggest that historic Euro-American disturbance probably induced conifer-to-hardwood state transitions at mid to high elevation coniferous ecological sites within the Appalachians. Where transitions have occurred, there appears to have been dramatic losses in forest floor thickness (O-horizons) and associated soil organic carbon stocks into atmospheric carbon pools. Spatial modeling of similar pedomemory properties and other soil-ecology linkages is likely to be a powerful tool to guide restoration in other regions as well.

Chemical quality of aboveground litter inputs for jack pine and black spruce stands along the Canadian Boreal Forest Transect Case Study

In the Canadian boreal forest, jack pine stands generally have a thin forest floor and occupy sites with coarsetextured soils and good drainage. Black spruce occurs more often on poorly drained sites and develops a thick mossdominated forest floor, but the common attribution of this development to poor quality of black spruce foliar litter has not been tested. We determined needle, twig, cone, and bark litter inputs during 10 y for black spruce and jack pine along the Boreal Forest Transect Case Study in northern Saskatchewan and Manitoba. Analysis of C, N, total phenolics, condensed tannins, and solid-state 13C NMR spectra from years 1–3 showed only small differences between species, notably higher tannins in black spruce cones. There was similarly little difference between area-based inputs, including classes of C structures determined by NMR. Condensed tannin input for black spruce was approximately twice that for jack pine, but both were in the very low range of reported values. Similar analyses showed that black spruce forest floor was less decomposed than that of jack pine, and for both species, aromatic litter C inputs appear to be poorly conserved, with a large influence of mosses and lichen. It is unlikely, however, that these large differences are mainly due to the small differences in aboveground litter inputs.

Effects of Biomass Removals on Site Carbon and Nutrients and Jack Pine Growth in Boreal Forests

As international demand for renewable energy and forest biomass increases, there is considerable debate about the effect of increased removals on long‐term soil productivity. Carbon and nutrient contents of the aboveground biomass, forest floor, and mineral soil were determined at 14 boreal forest sites in northern Ontario. At each site, three treatments were performed: tree‐length harvesting (OM0), full‐tree harvesting (OM1) and full‐tree harvesting plus forest floor removal (OM2). Theoretical and actual estimates of biomass removal for OM0 and OM1 were determined. Jack pine (Pinus banksiana Lamb.) dominant height increments from Years 10 to 15 (HD10‐15) were determined as a measure of site productivity. A nutrient budget approach was used to estimate C and nutrient removal and retention and to calculate stability ratios (i.e., ratio of nutrient removed during harvest to post‐harvest nutrient reserve) and nutrient replacement times. The OM1 treatment removed 65% of the potentially available biomass; on average 27 Mg ha−1 of unutilized biomass was burned in slash piles. The OM1 harvesting residue retention values coincided with guidelines of jurisdictions that recommend retaining one‐third of residues on site after bioenergy harvesting. The OM0 and OM1 C and nutrient removals were more similar than estimated in previous studies. Base cation stability ratios and nutrient replacement times gave opposite interpretations in terms of which sites were more sensitive to biomass removal treatments. For sandy sites with thin forest floor horizons HD10–15 responded positively to increased post‐harvest soil C reserves, but for sites with thick forest floors, organic matter accumulation became a detriment to increased growth.